98 Disco I - how to reset ABS light?

My Disco has been reliable until recently (80K miles on original Michelin 4x4 XPC). First it was water in ECU ($430), then I couldn't shift out of PARK (the brake-stop switch had to be replaced). Immediately after replacing the switch, ABS light came on. I think this is due to the brake-stop switch, which is part of the ABS circuit. Now I just need to reset the ABS light, right?

Anyway spent 2 evenings Googling about this, and found such a massive ABS-light problem reported by Land Rover Disco/RR owners, more infamous than Debbie from Dallas. What a shame! Worst is there is no good advise on how to deal with it - I gathered this is a complex problem, and you can go broke (or go crazy) if you try replacing bits by bits.

The car drives fine, but no opportunity to test to see if ABS is actually working. All I want to do is to reset the light. Some advised to jumper 2 pins on the ABS diagnostic connector to clear the code, but I was not able to find the connector in my 98 Disco I (Canadian model). Called dealer and was told one would need scantool (OBD) to reset the fault (or pay $100 to check it out) - bought one today ($130) but the OBD reader did not pulled up any fault codes (got GREEN light and no fault code).

Some suggest ignoring the light. What I worry about is not having ABS working, and I have been saved by ABS several times driving on icy mountain roads, particularly relying ABS to go downhill on icy roads.

It feels like I've reached the end of the Internet, as I can't find an easy instruction to clear the ABS light. I am looking for that one Land Rover technican who can answer this decade-old question, for all of the Disco owners.

Comments

Excellent article on the ABS problem by John Robison at RoversNorth .....

Welcome to the techie column for the Fall edition ofthe Rover News. In this column, we&#146;re going to lookat some of the common problems with the antilockbrakes on Discovery II models. The Discovery II electronicbraking system, called SLABS (self leveling antilock braking), is made by Wabco of Germany. Wabcois a subsidiary of American Standard, a company betterknown to the public for toilets than brakes. In theautomotive field, Wabco specializes in braking andsuspension systems for trucks. According to the company,two out of three commercial vehicles withadvanced braking systems are equipped with Wabcoproducts.The Land Rover system includes four-wheelantilock braking, hill descent control, and four-wheeltraction control. The SLABS control unit also controlsthe self-leveling suspension, if the vehicle has that feature.The Discovery air suspension is also a Wabcoproduct. As an aside, Wabco air suspension is alsofound in the new Audi A6 and the Mercedes CLS.One of the most common ABS questions Ihear is, Why do I see the ABS, TractionControl, and Hill Descent lights coming on?All three of those systems share a common set ofcore components. The wheel speed sensors, the hubs,the modulator, the controller, and other parts serve allthree systems. So a fault in any one of them will causea problem in the other two. It is actually rare to havea fault that would only disable one of the three systems.99% of the time, if one is affected, they all are.To see what&#146;s wrong, you will need to connect aLand Rover test system and read the faults. These systemsare not OBD II compatible, so a generic scannerwon&#146;t talk to them. At Robison Service, we use the T4or Autologic tools for this work.The most common faults are wheel speedsensor faults. The wheel speed sensors in a LandRover are coils that sense the motion of a toothedwheel that&#146;s a part of the wheel hub. The rotation ofthe wheel induces a sine wave signal in the sensorwhose frequency is proportional to the speed, andwhose amplitude increases with speed from 0.5 voltsto more than 5 volts.If your Rover has a speed sensor fault, there aretwo paths to repair. The first is to replace the entirehub on the affected corner. This is the approachfavored by dealers because the toothed wheel &#150; calleda reluctor ring &#150; and the actual sensor are both partof the hub. The reluctor can get damaged by rust orcorrosion, and it can also get damaged by a bad wheelbearing. The only way to service it is to change thehub.As of this writing, hubs (front-RND646 / rear-RND694)cost around $400 and take about three hours tochange.The sensor can be removed from the hub fairlyeasily. If you remove your sensor and look inside youshould be able to see if the reluctor ring is damaged.The reluctor ring can get damaged if the wheel bearinggets loose. It can also get damaged by corrosion.That&#146;s especially true for Rovers that run on beaches.If you see reluctor ring damage, or corrosion, or if thehub has any free play at all &#150; you need a completeassembly. If there is no damage, you may be able tofix the vehicle by changing the sensor (front-RN292 /rear-RNH293) alone, a $100 part that&#146;s less than an hourto swap.The path you choose should be determined byexamination of the reluctor via the sensor hole. If thehub looks good, there&#146;s an &#147;8 or 10&#148; odds that a sensoralone will fix your problem.Every now and then you will see a Rover that haswiring problems, usually at the connector between ABSsensor and body. Always pull it apart and look forcorrosion.The next common fault in these systemsis called shuttle valve failure. The shuttle valveis a part of the brake modulator &#150; that big thing in thelocation where a master cylinder would be. The modulatorincorporates the functions of an ABS servo anda brake master cylinder into one unit.If you have shuttle valve problems, you will seethe three warning lights on the dash and there will beone or more stored faults for shuttle valve failure.Land Rover has a test procedure to determine if thesefaults result from a failure in the modulator or if theyare caused by wiring troubles in the ABS harness orgrounds. Unless you have corroded grounds andcables, your trouble is probably in the modulator.Until now, this problem was addressed byreplacement of the brake modulator (RNH082). That&#146;s a$1,500 part. As you can imagine, shuttle valve failureproduced a lot of unhappy owners and Land Roverfinally listened up and developed a fix.As of March 2006, Land Rover sells a shuttlevalve repair kit for under $100. You will have toremove the modulator and flip it over to install thevalves on a workbench. Removal of the modulator,replacement of the valve, and refit to the vehicle takesthree hours or so.This shuttle valve repair is a huge improvementover the former method of addressing this problem.The part number for the repair kit is (SW0500030).If you buy it from a dealer you may also want to askfor the March 2006 bulletin that gives test and installationinstructions.Another common problem is a mushybrake pedal. In my experience, the only explanationfor a mushy pedal is improper bleeding procedure.Bleeding a Discovery II takes two people and the LandRover test system, and it takes the two of them a bitover half an hour. You need the tester to operate thepump and valves to make sure all the air is purgedfrom the modulator.If you are paying for this service, expect a laborbill in the range of one and a half hours and $20-30 ofbrake fluid. If you are not at a dealer, make sure theyuse the correct Castrol LMA fluid. Don&#146;t even start thisprocess unless the shop has a tester to run the pumpand valves. You could bleed brakes in the field withoutone in an emergency, but there is no way to get areally good pedal without cycling pump and valves.There is no shortcut for this job. You need twopeople and the Land Rover tester.We see quite a few stop lamp circuitproblems. The usual way this problem manifestsitself is a truck that won&#146;t shift out of park. DiscoveryII models have an interlock that prevents shifting outof park unless the brake is pressed. So, if the brakelight circuit fails, the car won&#146;t go into gear.If that happens to you, the first step is to checkthe stop lamp fuse. We&#146;ve seen several trucks wherethe stop lamps were fitted wrong, or the contacts corroded,and the fuse blew. Also check the trailer connector,if your Rover has one. A short there can popfuses.If the fuses are good, you should check the stoplamp switch. It&#146;s located above the brake pedal. Ifyou are stuck somewhere, it is possible to get out ofpark by jumping the switch temporarily with a paperclip.Finally, you should check your Rover tosee